taevakeha või satelliidi kõrvalekaldumine oma arvutuslikust orbiidist
a disturbance in the regular motion of a celestial body, resulting from a force that is additional to that which causes the regular motion, specifically a gravitational force
It is the elaborate developments of various perturbation theories and their applications to approximate the exact motions of celestial bodies that has occupied celestial mechanicians since Newton's time.
